Abstract
Biological soil crusts (BSC) encompassing green algae, cyanobacteria, lichens, bryophytes, heterotrophic bacteria and microfungi are keystone species in arid environments because of their role in nitrogen- and carbon-fixation, weathering and soil stabilization, all depending on the photosynthesis of the BSC. Despite their importance, little is known about the BSCs of the Atacama Desert, although especially crustose chlorolichens account for a large proportion of biomass in the arid coastal zone, where photosynthesis is mainly limited due to low water availability. Here, we present the first hyperspectral reflectance data for the most wide-spread BSC species of the southern Atacama Desert. Combining laboratory and field measurements, we establish transfer functions that allow us to estimate net photosynthesis rates for the most common BSC species. We found that spectral differences among species are high, and differences between the background soil and the BSC at inactive stages are low. Additionally, we found that the water absorption feature at 1420 nm is a more robust indicator for photosynthetic activity than the chlorophyll absorption bands. Therefore, we conclude that common vegetation indices must be taken with care to analyze the photosynthesis of BSC with multispectral data.
Highlights
In arid regions, biological soil crusts (BSCs) are keystone organism communities consisting of cyanobacteria, green algae, bryophytes, heterotrophic bacteria, microfungi and lichens [1]
The aims of the present study were three-fold: 1. We described for the first time the hyperspectral reflectance signal of BSCs in the Atacama Desert under different water availability conditions
We could demonstrate that hyperspectral reflectance signals among wide-spread species of BSCs in the Atacama Desert differed largely, but water content affected the spectra in a similar manner
Summary
Biological soil crusts (BSCs) are keystone organism communities consisting of cyanobacteria, green algae, bryophytes, heterotrophic bacteria, microfungi and lichens [1]. Many communities encompass species of two coalescing groups: the heterotrophic part is represented by fungi and the phototrophic component by cyanobacteria and/or eukaryotic green algae [2]. The heterotrophic part is responsible for the structure and water supply of the organism and protects the phototrophic organism against ultraviolet radiation by the production of pigments [3]. The phototrophic component provides carbohydrates from photosynthesis. In the case of the absence of water, the phototrophic component is in a dormant state. Under natural conditions where periods of desiccation and rehydration alter frequently, photosynthesis starts usually within seconds after water becomes available [4]
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